1. Field of the Invention
The invention relates to communications systems and more particularly a system for transmitting and receiving multiple TV signals through a common transponder.
2. Description of the Prior Art
Typical transponders, geostationary satellites for example, have limited bandwidth and power capabilities. The number of TV signals which can be simultaneously transmitted via a transponder can be increased if the bandwidth of the individual TV signals can be reduced.
Prior art systems for transmitting a plurality of TV signals through a common transponder included apparatus to delete selected lines of each of the signals and time-multiplex the remaining lines such that the lines of the signals did not overlap. This technique permitted a plurality of TV signals to be transmitted through a common transponder using the same bandwidth as one of the original signals. However, these systems required that the signals be synchronized so that no two signals would be simultaneously transmitted. This was necessary because if the signals overlapped the bandwidth or the transponder could be exceeded during a time interval corresponding to the overlap. The required synchronization was difficult to achieve if two or more of the signals being transmitted originated at different geographical locations.